The present invention relates to component packaging. More particularly, the present invention relates to a thermally insulative, hermetic or non-hermetic package for isolating optical components (e.g., arrayed waveguide gratings) from external stresses.
Fiber optic communication links have been conventionally employed in long-haul, point-to-point networks with controlled environments at all interface points. Such highly controlled, xe2x80x9ccentral officexe2x80x9d surroundings usually offer relatively benign operating environments (temperature, humidity, mechanical) for components. Consequently, highly functional components could be developed and installed without considering the impact of other, more extreme environments.
Recent technological advances, coupled with increasing bandwidth demand, are rapidly expanding the use of fiber optic components beyond the xe2x80x9ccentral officexe2x80x9d and into potentially harsher environments. For example, dense wavelength division multiplexing (DWDM) enables the transmission of multiple, independent wavelength streams across a single fiber. Predictably, this capability has resulted in the requirement to add or drop these optical channels along the previously untapped long lengths of fiber (and outside of the central office environment) to provide access to the individual wavelength streams. Optical add/drop multiplexers (OADMs) are employed for this function, enabled by arrayed waveguide grating (AWG) components for filtering and forwarding individual wavelengths.
In addition to these technological advances, simple market forces are pushing fiber networks beyond central offices and into the diverse terrain of xe2x80x9cmetroxe2x80x9d markets. This ever-increasing need for fiber bandwidth is resulting in the widespread deployment of fiber networks, and their associated components, into the harsher, less environmentally controlled conditions present in the metro market.
The demands placed on component designers now reach far beyond optical performance, and into the realms of thermal and mechanical insulation. Certain qualification standards (e.g., Telcordia) exist for reliability of optical components, and many customers require qualification under these standards. AWGs however are thin, fragile chips with narrow waveguides produced using planar lightwave circuit (PLC) processing techniques. The various processing tolerances required to meet the requisite optical specifications are already very tight, and in fact get tighter as the need to process more and closer channels increases.
There is also a need to maintain the tightly controlled, internal operating environment (e.g., temperature) for proper optical component operation in a package. The optical performance of PLC waveguides is especially sensitive to temperature. These components usually include active heating elements in closed loop feedback configurations to ensure temperature stability. It is therefore important to thermally insulate the package to ensure the PLC is kept at stable temperature by the heating element.
Environmentally secure packages therefore now play a vital role in the widespread commercialization of these devices. Without adequate packaging, components such as AWGs, with their highly unique and useful functions, would be relegated to laboratory environments only. It is difficult and costly to impose yet additional requirements on the chip process in the form of advanced materials, processing techniques, etc. to satisfy the harsher environmental standards discussed above.
What is required, therefore, are advanced packaging techniques to enable the widespread use of otherwise fragile optical components in diverse and often stressful environments, and which also maintain the internal operating temperature of these optical components to ensure their proper optical performance.
These requirements are met, and further advantages are provided, by the present invention which in one aspect is an optical component packaging technique, including the package itself, and its method of fabrication. According to the present invention, a transfer molded layer of material (e.g., syntactic foam in one embodiment) is formed at least partially around, or entirely around, the optical component to provide structural and thermal insulation around the component.
In one disclosed embodiment, the optical component comprises a planar lightwave circuit (PLC), with a protective passivation layer formed between the PLC and the layer of syntactic foam, to de-couple stresses and thermal transfer between the PLC and the layer of syntactic foam.
Strengthening caps, fiber assemblies, and a heater, may be provided with the PLC assembly, around which the layer of syntactic foam can also be formed. The protective passivation layer can also be formed between theses structures and the layer of syntactic foam; in one embodiment between at least two strengthening caps formed on opposing edges of the PLC.
The layer of syntactic foam can be formed around portions of, or entirely around, the PLC assembly, but allowing for the passage of fiber optics and/or control leads from the assembly.
In another aspect of the invention, at least one buffer structure encloses a first insulative cavity against a temperature-sensitive portion of the PLC, and separates the syntactic foam from this temperature sensitive portion. The buffer structure has a generally planar section with a frame projecting from its perimeter toward the component to form the cavity against the component.
The encompassing syntactic foam of the present invention structurally and thermally insulates the temperature-sensitive portions of the PLC from the outside ambient environment, and can be formed to be hermetic if required. The thermal isolation also reduces the power consumption required to maintain tight temperature control of the device and reduces thermally induced mechanical stresses which could negatively affect the device performance or reliability. A very small form-factor package is also possible using this approach.